Balancing machine

ABSTRACT

In a balancing machine for the measurement of, and compensation for, any unbalance of rotors, with a sliding bearing ( 1 ) for rotatably mounting a rotor ( 2 ) to be balanced and a supply device for supplying the sliding bearing ( 1 ) with a fluid, said sliding bearing ( 1 ) comprising a bearing shell ( 6 ) with a hollow cylindrical bearing face mounting a rotor section having a cylindrical sliding face, the bearing shell ( 6 ) is made of a hard ceramic material and the supply device is designed to supply the fluid in minimum amounts.

This invention relates to a balancing machine for the measurement of,and compensation for, any unbalance of rotors, in particularcrankshafts, with a sliding bearing for rotatably mounting a rotor to bebalanced and a supply device for supplying the sliding bearing with afluid, said sliding bearing comprising a bearing shell with a hollowcylindrical bearing face mounting a rotor section having a cylindricalsliding face.

In balancing machines different bearing arrangements for rotatablesupport are provided for the rotor to be balanced, depending on the typeand size of the rotor. Conventional bearing arrangements include, forexample, supporting roller bearings in which the rotor is placed onpairs of supporting rollers. Where lightweight rotors are involved, useis made of prism bearings made from a wide variety of materials, thepermissible compressive loads per unit area being however low. Forlightweight rotors provision can be made for an aerostatic oraerodynamic bearing. At high rotational speeds and with heavyweightrotors, sliding bearings are conventionally used as, for example,hydrostatic or hydrodynamic sliding bearings. As such, the bearingsemployed are frequently similar or identical to those in operatingcondition, being accurately designed to fit the bearing journal of therespective rotor.

In a balancing machine of the type initially referred to, which is knownfrom U.S. Pat. No. 1,486,115, the sliding bearing includes two spacedsegmental bearing shoes mounted on a support in such a manner as toenable them to execute limited rocking motions. The bearing shoes havepassageways terminating in the bearing face and communicating by meansof flexible conduits with a supply system for the supply of oil underpressure. On rotation of the rotor held in the bearing, a wedge-shapedoil film carrying the rotor is formed between the rotor and the bearingshoes.

A balancing machine with fluid-supplied sliding bearings is furthermoreknown from the printed publication B 1420 “Auswuchtmaschinen fürKurbelwellen” (balancing machines for crankshafts) of the Carl SchenckAG of Darmstadt. In this machine, during the measuring run the slidingbearings are lubricated with filtered coolant used for cooling thebalancing tool during the balancing operation.

In balancing machines the known sliding bearings supplied with fluidnecessitate considerable constructional expenditure because of the needto provide special equipment for splash protection and for encapsulatingthe fluid supply system relative to the environment.

It is also known to use ceramic materials for the manufacture of thesliding or bearing faces of sliding bearings. From DE 195 26 497 A1, forexample, a sliding bearing is known which has ceramic sliding membersfor the formation of a hydrodynamic lubricant wedge and a counteractingbearing face formed by a ceramic layer. Moreover, sintered compositematerials for the formation of mating pairs of sliding bearings areknown, with the composite materials having a pore volume sufficientlylarge to hold oil for bearing lubrication, cf. DE 38 22 919 A1, DE 42 14877 A1. In the known ceramic bearings or porous bearings the cooperatingsliding faces of the bearing partners are each of like or similarmaterial.

It is an object of the present invention to provide a balancing machineof the type initially referred to, which is of straightforwardconstruction, hence affording economy of manufacture, and isdistinguished by high measurement accuracy.

To accomplish this object, in the balancing machine of the invention thesliding bearing is provided with a bearing shell made of a hard ceramicmaterial, and the supply device for supplying the sliding bearing with afluid, in particular an aerosol or oil aerosol, is designed to supplythe fluid in minimum amounts.

According to the design of the invention, provision is made for asliding bearing receiving a minimum amount of fluid and having a hard,wear-resistant ceramic bearing shell with little inclination to seizeinstead of, for example, a hydrodynamic sliding bearing of the typeconventionally employed for carrying heavyweight rotors and at highspeeds. Surprisingly, it has been found that with a hard and smoothceramic bearing shell a very small amount of fluid is already sufficientto ensure a reliable lubricant and coolant supply. The bearing isoperated under mixed-friction conditions, meaning that there is nocomplete separation of the surfaces of rotor journal and bearing shell.Tribologically particularly advantageous is the combination of metallicrotor journal and ceramic bearing shell. It prevents adhesive wear(seizing) reliably, although the bearing face is supplied with a minimumamount of lubricant. The invention enables the lubricant and coolantsupply device to be reduced to a simple minimum-amount supply system,and the problems, in particular in terms of environmental compatibilitywhich are encountered with a hydrodynamic fluid lubrication, areavoided.

According to the invention, the supply quantity for a sliding bearing isof the order of a few milliliters per hour, whereas in hydrodynamicsliding bearings, for example, amounts of the order of liters per minuteare necessary. In the case of a fluid lubrication, special userspecifications concerning operating material have to be customarilyobserved, which may differ from user to user or also on a case-by-casebasis, which is advantageously not the case with the supply of theinvention. Furthermore, it avoids the problems, in particularenvironmental problems, which exist when oils are used as operatingfluids, in terms of fire, explosion and emission protection or waterpollution regulations. The present invention hence ensures anenvironmentally friendly operation.

With regard to the achievable balancing accuracy it is particularlyadvantageous that wetting of the rotor with lubricant and coolant, whichcorrupts the measurement result in particular of rotors that are notrotationally symmetrical such as crankshafts, is avoided reliably. It isanother advantage with respect to the achievable balancing accuracy thatthe bearing stiffness is not affected by a fluid film and hence by theangular velocity of the rotor. Furthermore, cost savings can be realizedin that the supply as with aerosol is readily adaptable to the differentoperating conditions.

As aerosol an oil aerosol is advantageously used, which involves feedingoil atomized in air in microscopically fine particles to the area to belubricated where it effects lubrication and, where applicable, alsocooling. Since an extremely fine oil mist is produced, economical use ofoil is ensured. The aerosol may also contain substances or additiveswhich allow, for example, a non-adhering solid-state lubrication orwhich may have an influence on a homogeneous atomization of the aerosol.

In one embodiment of the invention in which provision is made for anaerosol application within the bearing area of the bearing shell, thecontinued use of components of a hydrodynamic or hydrostatic bearing ispossible to advantage. This is also possible in cases where drip feed isused. Furthermore, the bearing shells are protected from contaminationby the injection of the aerosol or can be cleaned easily thereby or bythe injection of air, as and when necessary.

In a particularly simple embodiment provision is made for the fluidapplication to take place on the exposed surface of the rotor sectionthat is not surrounded by the bearing shell. For a spray application aswell as for a drip feed application, the discharge orifice of anatomizer and, respectively, the drip outlet can be positioned optimally.The spray application can be performed advantageously by a brief burstof the atomizer preferably at the beginning of the measuring run.

In order to ensure process security of the sliding bearing of thebalancing machine of the present invention, according to a furtherproposal of the invention provision can be made for temperaturemonitoring the sliding bearing or a bearing shell thereof. Owing to theincreasing friction between bearing shell and rotor journal, any failureof the minimum-amount lubrication will manifest itself in a rise intemperature and, accordingly, can be detected by temperature monitoringearly and be utilized for the initiation of remedial action.

On a single-station balancing machine in which the rotor is nottransferred between the measuring operation and the balancing operation,the discharge orifice of, for example, an atomizer or a drip feed devicecan be positioned advantageously at the bearing point during themeasuring operation for bearing lubricating and cooling purposes, andduring the balancing operation on the balancing tool for cooling andlubricating it. Considering that in such a machine several applicationsites have to be supplied with fluid, an economical consumption of thecoolant and lubricant can be ensured in the most simple manner.

In order to be able to feed aerosol, for example, to the bearing pointsand the balancing sites separately and consecutively, movable supplylines may be provided which allow positioning at the respectiveapplication site. It is also possible to provide supply lines for eachapplication site, which are adapted to be connected and disconnected.

When only selected application sites are be supplied as with aerosol,but also when all of them are to be supplied with aerosolsimultaneously, the significant advantage of a “dry” balancing machineresults which obviates the need to provide paneling such as splashguards or collection containers to collect dripping liquid. With theinvention a “dry” type of fluid lubrication during the operations ofboth determining unbalance and balancing is accomplished for the firsttime.

Advantageous embodiments of the present invention will be described ingreater detail in the following with reference to the accompanyingdrawing. In the drawing,

FIG. 1 is a sectional view of a bearing arrangement of the invention;and

FIG. 2 is a side view of an unbalance measuring and compensating device.

The bearing arrangement shown in FIG. 1 schematically comprises asliding bearing 1 for the rotor 2, a fluid supply device 3 designed tosupply minimum amounts of fluid, a control device 4 and a fluid pressuresupply 5. The bearing arrangement is part of an unbalance measuring andcompensating device, shown schematically in FIG. 2, for the rotor 2 andhas two bearing posts 8, 9 as bearing arrangements in which the rotor 2is carried with its bearing points 10, 11. For balancing, the rotor 2 isset in rotation in known manner, the out-of-balance vibrations occurringdue to the unbalance to be removed are measured and evaluated, and therotor 2 is balanced in predetermined compensation planes 12, 13 by theremoval of material at the balancing sites.

The bearing arrangements include bearing shells 6 shaped to conform tothe bearing journals of the rotor 2, which include the bearing points10, 11. To receive the bearing journal, the bearing shell 6 has a hollowcylindrical recess 7 with a pocket-shaped indentation 20 for applicationof the aerosol or of air to be blown through the bearing point. By meansof a control device 4 in the form of a directional control valve, thepocket-shaped indentation 20 communicates with either the fluid pressuresupply 5 or the minimum amount fluid supply device 3, or it is shut off.The bearing shell 6 is comprised of two self-aligning bearing elementsmade of a very hard ceramic material and has a very smooth bearing face.Osculation between the bearing shell 6 and the rotor 2 is at the bestpossible level.

The fluid supply device 3 is constructed as an aerosol atomizer.Alternatively or additionally, it is also possible for the fluid supplydevice 3 to be designed to dispense minimum amounts of a fluid to a dripfeeder or to supply a lubricating member which has its volumeimpregnated with fluid and is caused to make contact with the rotorsection 2 at periodic intervals. With the aerosol atomizer, fluid suchas oil is dispersed in air in minute particles and fed to a dischargeorifice in the pocket-shaped indentation 20 of the bearing shell 6. Forthis purpose, the aerosol atomizer is in communication with the fluidpressure supply 5 for the supply of air under pressure and, via thecontrol device 4, with the pocket-shaped indentation 20 during rotationof the rotor 2 in the measurement cycle, as shown schematically in theleft-hand section of the control device 4. Tests have surprisinglyrevealed that for the balancing of heavyweight rotors at high speedssmall amounts of aerosol in the range from about 1 to 100 ml/h areperfectly sufficient to reliably prevent any damage to bearing faces andexcessive heating; all that is required is an aerosol burst lastingabout 1 second at the beginning of the measuring run. As shownschematically in the right-hand section of the control device 4, whenrequired the fluid pressure supply may be connected directly with thepocket-shaped indentation 20 for the purpose of cleaning the bearingpoint by having air blown therethrough; the supply of aerosol is theninterrupted. It is however also possible for the bearing point to becleaned with aerosol.

For monitoring the operating temperature provision is made on thebearing shell 6 for a temperature sensor 21 connected to the machinecontrol by a line 22. This enables the instant release of an additionalamount of fluid for lubricating the sliding bearing as soon as theoperating temperature of the bearing exceeds a predetermined limitvalue. When the temperature continues to increase, the rotor may also bebrought to a standstill.

The unbalance measuring and compensating device, illustratedschematically in FIG. 2, of a balancing machine includes two bearingposts 8, 9 with bearing shells 6 of the type shown in FIG. 1 forrotatably mounting the rotor 2, and it has a lubricant and coolantsupply system communicating through ports 30, 30′ with a minimum amountfluid supply device for supplying an aerosol. The minimum amount fluidsupply device corresponds in principle to the device described withreference to FIG. 1. To compensate for the determined unbalance,balancing tools 32 are provided which remove rotor material at thebalancing sites in the compensation planes 12, 13.

The lubricant and coolant supply system has two conduit systems 31 and31′ for supplying different application sites. The conduit system 31′supplies aerosol to the bearing points 10 and 11, while the conduitsystem 31 feeds aerosol to the balancing sites and the balancing tools32 and 33. The discharge orifices of the supply lines of the conduitsystem 31′ are arranged close to the rotor sections, not surrounded bythe bearing shells 6, of the bearing points 10, 11, whereas thedischarge orifices of the supply lines of the conduit system 31 arearranged close to the compensation planes of the rotor 2.

Alternatively, the discharge orifices of the supply lines of the conduitsystem 31′ may be disposed within the bearing shells 6, as shown in FIG.1.

For economic use of the aerosol, the supply lines may be connected suchthat during the measurement cycle only the bearing points 10, 11 aresupplied with aerosol. Experience has shown that a brief burst ofaerosol at the beginning of the measuring run is sufficient. During thebalancing operation when the rotor 2 is at standstill aerosol issupplied exclusively to the balancing site where the balancing operationis in progress.

In an embodiment of the invention not shown in greater detail, provisionis made for the conduit system 31 to include a movable supply line whosedischarge orifice is in each instance positioned at the balancing sitewhere the balancing operation is being performed.

In another embodiment provision can be made for only one conduit systemwith two movable supply lines which are each associated with either thetwo bearing points 10, 11 or the two balancing sites and which duringthe measurement cycle supply aerosol to both bearing points 10, 11,while during the balancing operation supply is only to the balancingsite at which the balancing operation is being actually performed.

The present invention enables for the first time balancing machines ofthe “dry” type to be constructed which for the lubrication of bearingsand the cooling of tools are typically equipped with handling anddisposal devices for lubricants and coolants. Accordingly, therequirement of having to take measures serving to guard against splashesor to collect dripping liquid is completely obviated. The balancingresult is not affected by the accumulation of liquid on parts of therotor, which enhances the accuracy.

1. A balancing machine for the measurement of, and compensation for, anyunbalance of rotors, in particular crankshafts, with a sliding bearing(1) for rotatably mounting a rotor (2) to be balanced and a supplydevice for supplying the sliding bearing with a fluid, said slidingbearing (1) comprising a bearing shell (6) with a hollow cylindricalbearing face mounting a rotor section having a cylindrical sliding face,characterized in that the bearing shell (6) is made of a hard ceramicmaterial and the supply device is designed to supply the fluid inminimum amounts.
 2. The balancing machine as claimed in claim 1,characterized in that the minimum amounts of fluid are fed in the formof an aerosol, in particular an oil aerosol. 3-20. (canceled)
 21. Thebalancing machine as claimed in claim 1, characterized in that thesupply device feeds the minimum amounts of fluid intermittently.
 22. Thebalancing machine as claimed in claim 21, characterized in that air issupplied in the intervals.
 23. The balancing machine as claimed in claim1, characterized in that the amount of fluid supplied to the slidingbearing is in the range from 1 ml/h to 100 ml/h.
 24. The balancingmachine as claimed in claim 1, characterized in that provision is madefor the application of fluid to take place within the bearing area ofthe bearing shell (6).
 25. The balancing machine as claimed in claim 1,characterized in that provision is made for the application of fluid totake place in the area of the sliding face, not surrounded by thebearing shell (6), of the rotor section.
 26. The balancing machine asclaimed in claim 1, characterized in that fluid is applied by means of adrip feed device or an atomizer, in particular in the form of a briefburst.
 27. The balancing machine as claimed in claim 1, characterized inthat the ceramic material has a Vickers hardness of about 4,000 N/mm² orhigher.
 28. The balancing machine as claimed in claim 1, characterizedin that the bearing face of the bearing shell is very smooth, having inparticular a surface roughness of Ra<0.2.
 29. The balancing machine asclaimed in claim 1, characterized in that non oxide ceramic is providedas the ceramic material.
 30. The balancing machine as claimed in claim1, characterized in that the sliding face of the rotor section is madeof metal.
 31. The balancing machine as claimed in claim 1, characterizedin that the bearing shell includes several self-aligning bearingelements.
 32. The balancing machine as claimed in claim 1, characterizedin that the bearing face of the bearing shell and the sliding face ofthe rotor section have a high-grade osculation.
 33. The balancingmachine as claimed in claim 1, characterized in that the sliding bearingis provided with a temperature monitoring device.
 34. A balancingmachine with a supply system for lubricating and cooling fluids which isassociated with several application sites, according to claim 1,characterized in that the supply system is designed and arranged to feeda minimum amount fluid, in particular an aerosol or an oil aerosol, tothe sliding bearing (1) for mounting a rotor (2) to be balanced and to abalancing tool (32) for the removal of rotor material.
 35. The balancingmachine as claimed in claim 34, characterized in that the supply systemincludes supply lines (31, 31′) leading to each application site. 36.The balancing machine as claimed in claim 34, characterized in that thesupply system includes at least one movable supply line whose dischargeorifice is movable to different application sites.
 37. The balancingmachine as claimed in claim 36, characterized in that the movable supplyline is adapted to be associated with one or several bearing planes forthe rotor (2) and one or several compensation planes (12, 13) for therotor (2).
 38. The balancing machine as claimed in claim 34,characterized in that the supply lines are adapted to be connected anddisconnected in dependence upon the measuring or balancing operation.